Lectures on Dark Matter Physics (1603.03797v2)

Abstract: Rotation curve measurements provided the first strong indication that a significant fraction of matter in the Universe is non-baryonic. Since then, a tremendous amount of progress has been made on both the theoretical and experimental fronts in the search for this missing matter, which we now know constitutes nearly 85% of the Universe's matter density. These series of lectures, first given at the TASI 2015 summer school, provide an introduction to the basics of dark matter physics. They are geared for the advanced undergraduate or graduate student interested in pursuing research in high-energy physics. The primary goal is to build an understanding of how observations constrain the assumptions that can be made about the astro- and particle physics properties of dark matter. The lectures begin by delineating the basic assumptions that can be inferred about dark matter from rotation curves. A detailed discussion of thermal dark matter follows, motivating Weakly Interacting Massive Particles, as well as lighter-mass alternatives. As an application of these concepts, the phenomenology of direct and indirect detection experiments is discussed in detail.

• The paper presents a comprehensive review of dark matter physics, detailing evidence from galaxy rotation curves and the structure of dark halos.
• The paper outlines methodological approaches including WIMP freeze-out calculations and numerical simulations to probe dark matter properties.
• The paper discusses both direct and indirect detection strategies, highlighting techniques such as recoil measurements and Sommerfeld-enhanced annihilation searches.

An Overview of "Lectures on Dark Matter Physics"

Mariangela Lisanti, in her instructional series "Lectures on Dark Matter Physics", presents a comprehensive introduction to the field of dark matter (DM) physics, originally delivered at the TASI 2015 summer school. Targeted at advanced undergraduate and graduate students, these lectures aim to provide foundational knowledge on the theoretical and observational aspects that underpin current understanding and research directions in dark matter physics.

The Evidence for Dark Matter

Lisanti begins by addressing the astrophysical evidence for dark matter, particularly focusing on rotation curves of galaxies. Observations revealing the flattening of these curves serve as critical evidence for the existence of a non-baryonic matter component. This gravitational evidence allows the inference of a spherical dark matter halo enveloping baryonic matter, a significant leap from observable stellar distributions.

Mass and Interaction Paradigms

The lectures delve deeply into the potential particle physics properties of DM. Through thermodynamic equilibrium and freeze-out scenarios, Lisanti navigates the classic Weakly Interacting Massive Particle (WIMP) hypothesis. The "WIMP miracle", which refers to the alignment of weak-scale interaction cross-sections with observed cosmological densities, remains a key motivational framework. However, Lisanti also entertains mass possibilities extending beyond conventional WIMP parameters, considering lighter particles and potential extensions involving high DM self-interactions. The detailed exploration of the DM parameter space highlights the potential for both scalar and fermionic candidates, analyzed through a phase-space density formalism.

Detection Pathways: Direct and Indirect

Lisanti provides an analysis of the methodologies in direct and indirect detection searches. Direct detection aims at measuring the recoil energy from DM-nuclei interactions in terrestrial detectors, with experiments like Xenon100 laying stringent constraints. The review covers the technical considerations for calculating event rates, interaction cross-sections, and incorporates the impact of astrophysical velocity distributions. The challenges in the detection of DM interactions, particularly at low mass scales, are carefully addressed.

Moreover, indirect detection prospects are explored, emphasizing searches for annihilation products (such as gamma rays) from high-density regions. Particular attention is given to the role of the Sommerfeld enhancement, a quantum mechanical effect that can significantly amplify annihilation rates at low DM velocities, potentially reconciling theoretical predictions with observational data.

Simulations and Astrophysical Models

The text further evaluates the role of numerical simulations in understanding DM's astrophysical distribution, capturing the structural evolution from initial density perturbations to large halo formations. It discusses the Navarro-Frenk-White (NFW) profiles for describing these distributions but acknowledges possible deviations in the presence of baryonic processes. The interplay between theory and experiment is emphasized to approach uncertainties and validate models.

Future Directions and Implications

While foundational in scope, the lectures hint at future directions in dark matter research, pushing the boundaries of known physics. Theoretical advances or observational breakthroughs could dramatically alter existing paradigms and offer fresh insights into the nature of the dark sector. Acknowledging the inherent uncertainties, Lisanti encourages ongoing theoretical innovation alongside experimental developments across various platforms, advocating for a multi-pronged approach to this pervasive cosmic mystery.

In sum, Lisanti's lectures provide a critical resource for students and early-career researchers, integrating theoretical frameworks with empirical advancements. This collection serves not only as a primer to the field but also as a reminder of the intricate connections between diverse branches of physics necessary to unravel the mystery surrounding dark matter.